In the production of copper the normally low-grade sulfide ores are usually concentrated by flotation, the thus-produced slurry is dewatered, and the resultant substantially dry ore is smelted. After some thickening the slurry is normally passed through a vacuum filter to thicken it to a water content by weight of approximately 15%. Subsequent roasting of this still wet ore reduces its water content to a standard level of approximately 8.5%, at which level it is possible to smelt the ore.
The above-described two-stage dewatering is relatively expensive, mainly due to the use of the thermal drying step. Considerable energy is lost in the form of hot water vapor which is produced by roasting the relatively wet slurry, and no recovery method for this thermal energy is practical.